An ESR study of PMMA mechanoradicals and of their interaction with oxygen

Analysis of ESR spectra of mechanoradicals from poly(methyl methacrylate) reveals that after mechanical degradation in vacuo at 77°K, the sample contains two types of primary radicals? CH₂? C(CH₃)(COOCH₃) (I) and CH₂? C(CH₃)(COOCH₃)? CH₂ (II) produced by the breaking of the polymer chain, and secondary radicals ? CH₂? C(CH₃)(COOCH₃)? CH? C(CH₃)? (COOCH₃)? CH₂? (III). With increasing temperature, radical I remains stable while II reacts with methylene hydrogen of the polymer chain giving rise to the secondary radical III, which decays and finally disappears as the temperature rises. After admission of oxygen at 113°K, the polymer radicals react with oxygen with formation of polymer peroxy radicals ROO. and diamagnetic dimers. With increasing temperature the latter dissociate again to the original polymer peroxy radicals which gradually decay, if the temperature is increased further. The present results are compared with earlier ones obtained on poly(ethylene glycol methacrylate) (PGMA).     

Free radicals in γ-irradiated poly-α-methylstyrene

Electron spin resonance (ESR) spectra were observed at ?160°C and at room temperature for γ-irradiated poly-α-methylstyrene. The spectrum observed at room temperature has been attributed to the radical species while that at ?160°C results from the same radical and superposition of the spectrum due to the radical ?H₂-C(CH₃)(C₆H₅)-. The radicals which are stable at room temperature could be used to graft vinyl acetate.     

Thermoluminescence of irradiated polystyrene

Thermoluminescence of irradiated polystyrene has been studied in the temperature range 100 to 440°K. Three glow peaks with maximum at 160, 221, and 378°K have been observed. These peaks are analyzed by different methods and the activation energies which were obtained are compared. The activation energies are found to be 0.22, 0.48, and 1.45 eV for the peaks with maxima at 160, 221, and 378°K, respectively. Second-order kinetics is appropriate to all these cases. The glow peaks are attributed to the decay of the free radicals formed on irradiation and subsequent thermal stimulation. The peak with the maximum at 160°K is attributed to electron trapping by the carbonyl groups or peroxy radicals formed on irradiation. The curve with the peak at 221°K is attributed to the cyclohexadienyl radical, and the curve with the peak at 378°K is attributed to the chain radical ? CH₂? C (C₆H₅)? CH₂? . The centers responsible for the observed thermoluminescence are identified by correlation with electron spin resonance (ESR) data obtained on the same samples.     

Radiolyse des hydrocarbures. 21e communication. Mécanismes radicalaires et non-radicalaires dans les n-alcanes en phase liquide

Contributions of radical and non-radical processes have been determined in the formation of radiolysis products of n-heptane, n-octane, n-nonane and n-decane in a large range of temperature. Calculations are based on the combination and the dismutation of radicals, both reactions having nearly the same importance. Hydrogen abstraction reactions become important above – 25°. Intermediate molecular weight products and dimers are formed by statistical combination of the various radicals resulting from C? C and C? H scission. At low temperature, low molecular weight products are formed by both radical and non-radical processes, the second one being more important (3/4 for alcanes and 2/3 for olefins). The yield of radicals increases with the chain length of the irradiated n-alkane and amounts to 4.5 for n-heptane and 6.8 for n-decane at – 25°. This increase is due only to radicals from C? H scission, while the yield of radicals from C? C scission remains constant. Scission of CH₂? CH₂ bonds is favored for bonds inside the molecule, but this affect diminishes with chain length and CH₂? CH₂ rupture is equally probable at all positions for n-alcanes heavier than decane. Methyl C? H scission is 2.7 times less probable than methylene C? H scission. The radiolysis of mixtures of protonated and deuterated n-alcanes is shown to be able to give information concerning basic processes in radiation chemistry.     

ESR study of the generation and decay of peroxy radicals in mechanically destructed polyamide 6

Polyamide 6 has been mechanically destructed in vacuo. At -70°, the ESR spectrum corresponds to the sum of the component spectra of three radicals NH?HCH₂, ·CH₂NHCO, and ·CH₂CONH. After introducing air into the ampoule, the spectrum changes even at -70°; the changes have been studied up to 0°. The spectrum of the peroxy radical ROO· (with line width 1.57 mT, g₁ = 2.0089 and g_| = 2.0301) predominates.     

ESR study on radical conversions in irradiated low-density polyethylene

ESR studies were carried out on radical conversions by thermal and photochemical mechanisms in low-density polyethylene irradiated mainly with electron beams at ?196°C both in vacuum and in the presence of CO. According to the spectral change, the following radical conversions were elucidated for the samples irradiated in vacuo [eqs. (1) and (1′)] and in the presence of CO [eqs. (2) and (2′)]. From the resemblance of the ESR spectrum observed after direct photolysis of polyethylene to that observed after photo-induced radical conversions of the allylic radicals, it is concluded that an eight-line ESR spectrum observed immediately after photolysis of polyethylene at ?196°C could be attributed more reasonably to the alkyl radicals ? CH₂CHCH₃ than to ? CH₂CH₂ and ? CH₂CHCH₂? .     

Electron Paramagnetic Resonance Study of Radical Pairs and Isolated Radicals Trapped in Irradiated Long-Chain Hydrocarbons at Low Temperatures

The intrinsic characteristics of radical pairs produced in squalane and in cetane receiving high gamma-dose are extensively studied with the EPR technique at temperatures from 77°K up to 150°K. The spectra of the paired radicals occur at g=4 with a very low transition probability in contrast to that of isolated radicals which appear at g=2 A well-resolved hyperfine spectrum corresponding to the species (CH₃CH₂.CH₂CH₃) is observed in cetane. The isothermal decay rates of radical pairs in cetane below 100°K are significantly slow; however, the decay kinetics at 150°K is first order with rate constant=1.86 min^?1. A relatively slower decay rate is obtained for isolated radicals suggesting that the decay mechanism of paired radicals is through geminate recombination. The relative inter-radical distance in radical pairs is known from a decay curve as a function of temperature. The yields of radical pairs are low in both matrices, only few percents of those of isolated radicals. The formation mechanisms of paired radicals with direct radiolytic bond scission process are discussed in connection with the experimental observations.     

Kinetics of the I2-catalyzed isomerization of allyl chloride to cis- and trans-1-chloro-1-propene. The stabilization energy of the chloroallyl radical

The I₂-catalyzed isomerization of allyl chloride to cis- and trans- l-chloro-l-propene was measured in a static system in the temperature range 225–329°C. Propylene was found as a side product, mainly at the lower temperatures. The rate constant for an abstraction of a hydrogen atom from allyl chloride by an iodine atom was found to obey the equation log [k,/M^?1 sec^?1] = (10.5 ± 0.2) ?; (18.3 ± 10.4)/θ, where θ is 2.303RT in kcal/mole. Using this activation energy together with 1 ± 1 kcal/mole for the activation energy for the reaction of HI with alkyl radicals gives DH⁰ (CH₂CHCHCl? H) = 88.6 ± 1.1 kcal/mole, and 7.4 ± 1.5 kcal/mole as the stabilization energy (SE) of the chloroallyl radical. Using the results of Abell and Adolf on allyl fluoride and allyl bromide, we conclude DH⁰ (CH₂CHCHF? H) = 88.6 ± 1.1 and DH⁰ (CH₂CHCHBr? H) = 89.4 ± 1.1 kcal/ mole; the SE of the corresponding radicals are 7.4 ± 2.2 and 7.8 ± 1.5 kcal/mole. The bond dissociation energies of the C? H bonds in the allyl halides are similar to that of propene, while the SE values are about 2 kcal/mole less than in the allyl radical, resulting perhaps more from the stabilization of alkyl radicals by α-halogen atoms than from differences in the unsaturated systems.     

Comparison of photo- and radiation-induced radical formation in polyethylene by ESR spectroscopy

The behaviors of free radicals produced in polyethylene irradiated with ultraviolet light and electron beams were compared in connection with primary processes of radical formation and trapping regions of free radicals. In the case of irradiation with ultraviolet light, an ESR spectrum observed at ?196°C immediately after irradiation is an eight-line spectrum due to alkyl radicals of the type ? CH₂? ?H? CH₃, while in the case of ionizing radiation, a six-line spectrum due to ? CH₂? ?H? CH₂? was observed. The former radicals are produced by the Norrish type I reaction of the carbonyl groups contained in the polymer, followed by radical rearrangement; and the latter are formed by dissociation of hydrogen atom from the excited state of the polymer or ion-molecular reactions. From the sensitivity to oxygen molecules, it was deduced that free radicals are trapped in amorphous regions after ultraviolet irradiation, but mainly in crystalline regions after irradiation with electron beams. Saturation studies of ESR spectra seem to support this conclusion.     

Reactions of methyl radicals with acetaldehyde and acetaldehyde-d1. II. BEBO calculations of the temperature dependence of the rate constants

The BEBO method was used to calculate the kinetic isotope effect for formyl-hydrogen abstraction from acetaldehyde by methyl radicals. The calculated isotope effect and experimental ratios of the rate constants obtained at 785°K for the reactions of CH₃ with CH₃CHO and CH₃CDO, together with the theoretical temperature dependence of the specific rates (as formulated by the BEBO theory), were used to obtain rate constants for the steps CH₃ + CH₃CHO → CH₄ + CH₃CO (2a), CH₃ + CH₃CHO → CH₄ + CH₂CHO (2b), and CH₃ + CH₃CDO → CH₃D + CH₃CO (1a) between 298 and 1224°K. It was shown that the curvature apparent in the Arrhenius plot of the rate coefficient k₂ reported for the reaction of methyl radicals with acetaldehyde in the temperature range of 298–1224°K is caused both by the simultaneous contribution of steps (2a) and (2b) to methane formation, and by the curvature in the Arrhenius plots of the two elementary rate constants themselves. The predicted curve agrees well with the experimental data, especially if the tunneling correction is applied.     

Ab initio studies of structural features not easily amenable to experiment. 25. Conformational analysis of methyl propanoate and comparison with the methyl ester of glycine

The molecular geometries of three conformations of methyl propanoate (MEP) (C? C? C?O torsions of 0°, 120°, and 180°) and the potential-energy surfaces of MEP (C? C? C?O torsions) and of the methyl ester of glycine (MEG) (N? C? C?O torsions) have been determined by ab initio gradient calculations at the 4-21G level. MEP has conformational energy minima at 0° and 120° of the C? C? C?O torsion, while the 60–90° range and 180° are energy maxima. For MEG there are two minima (at 0° and 180°) and one barrier to N? C? C?O rotation in the 60–90° range. The N? C? C?O barrier height is about twice as high (4 kcal/mol) as the C? C? C?O barrier. The 180° N? C? C?O minimum is characteristically wide and flat allowing for considerable flexibility of the N? C? C?O torsion in the 150–210° range. This flexibility could be of potential importance for polypeptide systems, since the N? C? C?O angles of helical forms are usually found in this region. The molecular structures of the methyl ester group CH₃OC(?O)CHRR′ in several systems are compared and found to be rather constant when R ? H and R′ ? H, CH₃, CH₃CH₂; or when R ? NH₂ and R′ ? H, CH₃, or CH(CH₃)₂.     

Electron spin resonance studies of polycarbonate irradiated by γ-rays and ultraviolet light

Paramagnetic species produced in polycarbonate (PC) by γ- or ultraviolet irradiation were investigated by ESR. In γ-irradiation, scissions of carbonate groups in the main chain occur. ESR spectra (g = 2.003₄) composed of a sharp singlet, some broad singlets, and a small signal with hyperfine structure are obtained, and they are assigned to trapped electrons, positive radical ions, phenoxy-type free radicals, phenyl radicals, and ? O? C₆H₄? C(CH₃)₂ radicals. The G value for total yields of paramagnetic species at 77°K is 1.8. The percentage of CO and CO₂, the dominant gases evolved, is 65.4 and 33.8%, respectively. In ultraviolet irradiation, energy is absorbed selectively at the surface region. The surface region becomes insoluble in methylene chloride because of crosslinking of phenyl groups. The ESR spectrum obtained at 77°K is a broad singlet and assigned to phenoxy-type free radicals, phenyl radicals, and polyenyl-type free radicals. Some differences in effects of γ- and ultraviolet irradiation of PC are discussed.     

Very low-pressure pyrolysis (VLPP) of pentynes. II. 4-methylpent-2-yne and 4,4-dimethylpent-2-yne. Heats of formation and resonance stabilization energies of methyl-substituted propargyl radicals

Studies of the unimolecular decomposition of 4-methylpent-2-yne (M2P) and 4,4-dimethylpent-2-yne (DM2P) have been carried out over the temperature range of 903–1246 K using the technique of very-low pressure pyrolysis (VLPP). The primary reaction for both compounds is fission of the C? C bond adjacent to the acetylenic group producing the resonance-stabilized methyl-substituted propargyl radicals, CH₃C??H(CH₃) from M2P and CH₃C?C?(CH₃)₂ from DM2P. RRKM calculations were performed in conjunction with both vibrational and hindered rotational models for the transition state. Employing the usual assumption of unit efficiency for gas-wall collisions, the results show that only the rotational model with a temperature-dependent hindrance parameter gives a proper fit to the VLPP data over the entire experimental temperature range. The high-pressure Arrhenius parameters at 1100 K are given by the rate expressions log k₂ (sec^?1) = (16.2 ± 0.3) ? (74.4 ± 1.5)/θ for M2P and log k₃ (sec^?1) = (16.4 ± 0.3) ? (71.4 ± 1.5)/θ for DM2P where θ = 2.303RT kcal/mol. The A factors were assigned from the results of recent shock-tube studies of related alkynes. Inclusion of a decrease in gas-wall collision efficiency with temperature would lower both activation energies by ～1 kcal/mol. The critical energies together with the assumption of zero activation energy for recombination of the product radicals at 0 K lead to DH⁰[CH₃CCCH(CH₃)? CH₃] = 76.7 ± 1.5, ΔH_f⁰[CH₃CCCH(CH₃)] = 65.2 ± 2.3, DH⁰[CH₃CCCH(CH₃)? H] = 87.3 ± 2.7, DH⁰[CH₃CCC(CH₃)₂? CH₃] = 72.5 ± 1.5, ΔH[CH₃CC?(CH₃)₂] = 53.0 ± 2.3, and DH⁰[CH₃CCC(CH₃)₂? H] = 82.3 ± 2.7, where all quantities are in kcal/mol at 300 K. The resonance stabilization energies of the 1,3-dimethylpropargyl and 1,1,3-trimethylpropargyl radicals are 7.7 ± 2.9 and 9.7 ± 2.9 kcal/mol at 300 K. Comparison with results obtained previously for other propargylic radicals indicates that methyl substituents on both the radical center and the terminal carbon atom have little effect on the propargyl resonance energy.     

Effect of lateral bromo substituent on the phase behavior of four-ring azo/ester/azo liquid crystalline materials

ABSTRACT

In order to study the influence of lateral Br substitution on mesophase behaviour, five homologous series of 4-substituted phenylazo phenyl 4?-(3?-bromo-4?-alkoxyphenylazo) benzoates (In_a–e) have been synthesised. Within each homologous series, the alkoxy group varies from 6 to 16 carbons, while other terminal group substituents, X, are CH₃O, CH₃, H, Br and NO₂ groups; the mesophase behaviour of these series is compared with previously prepared laterally neat analogues, 4-substituted phenylazo phenyl 4?-(4?-alkoxyphenylazo) benzoates (IIn_a–e) and laterally methyl analogues, 4-substituted phenylazo phenyl 4?-(3?-methyl-4?-alkoxyphenylazo) benzoates (IIIn_a–e). Similar to lateral methyl analogues, the present series, lateral Br substitution showed that, independent of the polarity of the substituent X or the alkoxy-chain length, the nematic phase is predominant with relatively high stability and broad temperature ranges. The mesophase stability varies between 204.0°C and 335.0°C for the nematic phase and 169.6°C and 281.0°C for the SmA phase. Their total mesophase temperature ranges vary between 87.2°C and 201.4°C. All compounds were found to be thermally stable within the mesophase temperature range, except the lower homologue of the nitro and Br substituted derivatives. The obtained results are discussed in terms of molecular polarisability.     

Ir spectra of complexes of n- and s-butyllithium with electron donors

Complexes of n- and s-butyllithium (BL) with THF, (CH₃)₂O and (CH₃)₃N have been investigated over a wide temperature range (+20 to ?100°C). These electron donors (D) are much less actively complexed with s-BL than with n-BL. For both alkyllithium compounds the trend of D to complexation decreases in the following order: THF > (CH₃)₂O > (CH₃)₃N. Usually, for the n-BL/D systems several complexes coexist with different Li/D ratios. At low temperatures and at the n-BL/D ratio ? 4, in addition to complexes with the limiting stoichiometry (n-BL)₄ · 4D, associates complexed with one D molecule and a hexamer n-BL are present. The bands of ν(CLi) stretching vibrations for s-BL complexes are not very characteristic and therefore only the average stoichiometry of the complex can be evaluated; the limiting stoichiometry detected was (s-BL)₄ · 4D. It is supposed that as the temperature decreases the inversion of the molecules of s-BL occurs during their interaction with excess ethers.     

Theoretical study of the effects of substitution,solvation, and structure on the interaction between nitriles and methanol

We report an investigation on intermolecular interactions in R? CN ··· H? OCH₃ (R = H, CH₃, F, Cl, NO₂, OH, SH, SCH₃, CHO, COCH₃, CH₂Cl, CH₂F, CH₂OH, CH₂COOH, CF₃, SCOCH₃, SCF₃, OCHF₂, CH₂CF₃, CH₂OCH₃, and CH₂CH₂OH) complexes using density functional theory. The calculations were conducted on B3LYP/6‐311++G** level of theory for optimization of geometries of complexes and monomers. An improper hydrogen bonding (HB) in the H₃CO? H ··· NC? R complexes was observed in that N atom of the nitriles functions acts as a proton acceptor. Furthermore, quantum theory of “Atoms in Molecules” (AIM) and natural bond orbital (NBO) method were applied to analyze H‐bond interactions in respective complexes. The electron density (ρ) and Laplacian (?²ρ) properties, estimated by atoms in molecules calculations, indicate that H ··· N bond possesses low ρ and positive ?²ρ values, which are in agreement with partially covalent character of the HBs, whereas O? H bonds have negative ?²ρ values. In addition, the weak intermolecular force due to dipole–dipole interaction (U) is also considered for analysis. The examination of HB in these complexes by quantum theory of NBO method fairly supports the ab initio results. Natural population analysis data, the electron density, and Laplacian properties, as well as, the ν(O? H) and γ(O? H) frequencies of complexes, calculated at the B3LYP/6‐311++G** level of theory, are used to evaluate the HB interactions. The calculated geometrical parameters and conformational analysis in water phase solution show that the H₃CO? H ··· NC? R complexes in water are more stable than that in gas phase. The obtained results demonstrated a strong influence of the R substituent on the properties of complexes. Numerous correlations between topological, geometrical, thermodynamic properties, and energetic parameters were also found. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Reactions of photogenerated fluorine atoms with dopant molecules in solid argon

The products of UV photolysis of ternary Ar?CH₄(CD₄)?F₂ mixtures (1:c:c ₀,c, c ₀=0.001–0.01) at 13–16 K were identified by ESR and FTIR spectroscopy. These products are^?CH₃ (^?CD₃) radicals of typesI andII and molecular CH₃F?HF complexes. The latter were characterized by the IR bands of the stretching C?F (1003 cm^?1) and H?F (3774 cm^?1) vibrations. The ESR spectra of radicalsI are asymmetric. The anisotropy of theg-factor (Δg～10^?3) of radicalI indicates that the structure of the radicals is nonplanar. The ESR spectrum of the typeII radical is identical to that of matrix-isolated^?CH₃ (^?CD₃) radicals with the planar structure (Δg<5·10^?5). Under the experimental conditions, the amount of complexes formed in the photolysis is equal to 0.022·c. When the photolysis is ceased, radicalI disappears after ≈10³ s and radicalII is stabilized. The limiting concentrations of the stabilized^?CH₃ and^?CD₃ radicals are equal to 2·10^?2·c and 2·10^?3·c, respectively. A mechanism of the formation of the products is suggested. It is based on the assumption that both matrix-isolated CH₄ and F₂ and their heterodimers CH₄?F₂ are present in the samples and it takes into account the long-range migration of translationally excited flourine atoms. The CH₃F?HF complexes and radicalsI are generated by the photolysis of the CH₄?F₂ heterodimers. The decay of radicalsI is caused by geminate recombination of proximate F...CH₃ pairs. RadicalsII are formed in the reaction of translationally excited fluorine atoms with isolated CH₄ (CD₄) molecules.     

Gemischtligandkomplexe des Rheniums. V. Die Bildung von Nitrenkomplexen durch Kondensation von Aceton an koordinierten Nitridoliganden. Darstellung und Strukturen von fac-[Re{NC(CH3)2CH2C(O)CH3}X3(Me2PhP)2]-Komplexen (X = Cl,Br)

Mixed-ligand Complexes of Rhenium. V. The Formation of Nitrene Complexes by Condensation of Acetone at Coordinated Nitrido Ligands. Syntheses and Structures of fac-[Re{NC(CH₃)₂CH₂C(O)CH₃}X₃(Me₂PhP)₂] Complexes (X = Cl, Br) The reaction of rhenium(V)-mixed-ligand complexes of the general formula [ReN(Cl)(Me₂PhP)₂(R₂tcb)] (HR₂tcb = N? (N,N-dialkylthiocarbamoyl)benzamidine) with HCl or HBr in acetone initializes a condensation of the solvent and results in nitrene-like compounds as a consequence of a nucleophilic attack of the coordinated nitrido ligand on the condensed acetone. The chelate ligands are removed during this reaction and complexes of the type fac-[Re{NC(CH₃)₂CH₂C(O)CH₃}X₃(Me₂PhP)₂] (X = Cl, Br) are formed. fac-[Re{NC(CH₃)₂CH₂C(O)CH₃}Cl₃(Me₂PhP)₂] crystallizes triclinic in the space group P1, a = 8.575(4); b = 9.088(3); c = 18.389(9) Å; α = 75.67(3)°, β = 85.30(3)°, γ = 70.58(4)°; Z = 2. A final R value of 0.031 was obtained on the basis of 6011 independent reflections with I ≥ 2σ(I). Rhenium is coordinated in a distorted octahedral environment with the three chloro ligands in facial positions. The rhenium-nitrogen bond (1,68(1) Å) is only slightly longer than typical Re? N bonding distances in nitrido complexes. fac-[Re{NC(CH₃)₂CH₂C(O)CH₃}Br₃(Me₂PhP)₂] is isomorphous with the chloro complex. Triclinic cell with a = 8.625(4); b = 9.198(3); c = 18.581(5) Å; α = 75.62(3)°, β = 85.40(3)°, γ = 70.91(3)°; Z = 2. The R value converged at 0.049 on the basis of 3644 independent reflections with I ≥ 2σ(I). fac-[Re{NC(CH₃)₂CH₂C(O)CH₃}Cl₃(Me₂PhP)₂] as well as fac-[Re{NC(CH₃)₂CH₂C(O)CH₃}Br₃(Me₂PhP)₂] crystallizes in the noncentrosymmetric space group P1.     

Very low-pressure pyrolysis (VLPP) of but-1-yne the heat of formation and stabilization energy of the propargyl radical

The unimolecular decomposition of but-1-yne has been investigated over the temperature range of 1052° – 1152°K using the technique of very low-pressure pyrolysis (VLPP). The primary process is C? C bond fission yielding methyl and propargyl radicals. Application of RRKM theory shows that the experimental rate constants are consistent with the highpressure Arrhenius parameters given by where θ = 2.303 RT kcal/mol. The parameters are in good agreement with estimates based on shock-tube studies. The activation energy, combined with thermochemical data, leads to DH°[HCCCH₂? CH₃] = 76.0, ΔH(HCC?CH_2,g) = 81.4, and DH° [HCCCH₂? H] = 89.2, all in kcal/mol at 300°K. The stabilization energy of the propargyl radical SE° (HCC?CH₂) has been found to be 8.8 kcal/mol. Recent result for the shock-tube pyrolysis of some alkynes have been analyzed and shown to yield values for the heat of formation and stabilization energy of the propargyl radical in excellent agreement with the present work. From a consideration of all results it is recommended that ΔH(HCC?CH_2,g) = 81.5±1.0, DH[HCCCH₂? H] = 89.3 ± 1.0, and SE° (HCC?CH₂) = 8.7±1.0 kcal/mol.     

Electron spin resonance study of poly-3,3-bis-(chloromethyl)oxetane irradiated with ultraviolet light

When poly-3,3-bis(chloromethyl)oxetane has been irradiated at ?196°C in a nitrogen atmosphere with ultraviolet light, a triplet spectrum is observed. After warming the sample, both a doublet and a singlet ESR spectra are observed. These spectra are attributed to and ? CH₂? O, respectively. The formation mechanism of these free radicals is discussed. It is concluded that the main process of radical formation is the dissociation of chemical bonds from the excited state of the polymer produced through the energy absorption by irregular groups acting as sensitizers. In the presence of oxygen, the radical yield at ?196°C is greater than that in nitrogen atmosphere. This is attributed to the extra absorption of light by the charge transfer complexes of polymers with oxygen molecules. It is also proposed that participation of a charge transfer complex in photooxidation of ether is important in the primary radical formation step. When a polymer sample irradiated in vacuum with ultraviolet light is treated at ?78°C for a few minutes in the presence of air, peroxy radicals form. This shows that oxygen molecules diffuse very easily into this polymer, even at this low temperature.